U.S. Pat. No. 5,561,742 corresponding to Japanese Patent Publication No. 2895672 discloses a multiple-robot control method for avoiding interference between a plurality of robots when they are commanded so as to be operated at the same time.
In the method disclosed in the U.S. Patent Publication, FIG. 9 is a top plan view schematically illustrating first and second robots RA and RU respectively mounted on a common plane through bases Sa and Sb. The first and second robots are schematically illustrated as vertical articulated robots, and the bases Sa and Sb are schematically illustrated as circles.
In FIG. 9, reference characters Aa and Ab respectively denote first and second arms of the first and second robots RA and RB, and reference characters Wa and Wb respectively denote wrist portions of the first and second robots RA and RB. Each of the wrist portions Wa and Wb consists of a wrist and a hand.
As illustrated in FIG. 9, a line connecting the centers of the bases Sa and Sb is regarded as a Y-axis, and a line on the common plane and perpendicular to the Y-axis is regarded as an X-axis, and a direction orthogonal to the common plane (X-Y plane) is regarded as a Z-axis. Thus X-Y-Z coordinate system is defined.
The first and second robots RA and RB are programmed to be simultaneously operated.
In the method, an operation command is sent to a controller (not shown) of both the first and second robots RA and RB. The operation command allows the controller to control the first robot RA so that the wrist portion Wa of the first arm Aa of the robot RA moves toward a target position PA to be located thereat. Simultaneously, an operation command is sent to the controller. The operation command allows the controller to control the second robot RB so that the wrist portion Wb of the second arm Ab of the robot RB moves toward a target position PB to be located thereat.
In FIG. 9, a sphere Cha represents a region covering the wrist portion Wa consisting of the wrist and the hand of the first arm Aa and located at the target position PA. Similarly, a sphere Chb represents a region covering the wrist portion consisting of the Wrist and the hand of the second arm Ab and located at the target position PB.
At that time, the controller obtains an X-Z plane Pa set to a position (Y-coordinate value), and defines a first robot's special region MA based on the X-Z plane Pa such that the X-Z plane Pa contacts the sphere Cha and receives it within the first robot's special region MA.
Simultaneously, the controller obtains an X-Z plane Pb set to a position (Y-coordinate value), and defines a second robot's special region MB based on the X-Z plane Pb such that the X-Z plane Pb contacts the sphere Chb and receives it within the second robot's special region MB.
The controller determines whether the obtained first robot's special region MA and the second robot's special region MB are at least partially overlapped with each other.
For example, as illustrated in FIG. 9, the first robot's special region MA and the second robot's special region MB are overlapped to each other.
For this reason, the controller brakes the motion of one of the first and second robot arms Aa and Ab at the timing when it is determined that the first robot's special region MA and the second robot's special region MB are at least partially overlapped to each other.
In other words, the controller prevents one of the robot arms Aa and Ab from moving so that one of the robot arms Aa and Ab is kept at rest while moving the other of the robot arms Aa and Ab toward the corresponding target position. The controller repeatedly executes the determination.
Thereafter, when, because of movement of the other of the robot arms Aa and Ab, it is determined that the obtained first robot's special region MA and the second robot's special region MB are separated from each other, the controller restarts to move one of the robot arms Aa and Ab toward the corresponding target position.
In the method, however, although the wrist portions Wa and Wb of the first and second robot arms Aa and Ab may interfere with each other only when they simultaneously enter the respective special regions MA and MB, each time it is determined that the first robot's special region MA and the second robot's special region MB are at least partially overlapped with each other, the controller brakes the motion of one of the first and second arms Aa and Ab, and keeps it at rest.
Accordingly, the method may increase the length of time before the wrist portions Wa and Wb of the first and second robots RA and RB are completely transferred to the corresponding target positions PA and PB, respectively.